Redshift Academy

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Astronomy

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Astronomical Distance Units .

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Celestial Coordinates .

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Celestial Navigation .

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Location of North and South Celestial Poles .

Chemistry

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Avogadro's Number .

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Balancing Chemical Equations

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The Periodic Table .

Classical Mechanics

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Blackbody Radiation .

Classical Physics

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Archimedes Principle

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Bernoulli Principle

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Center of Mass Frame

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Comparison Between Gravitation and Electrostatics

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Compton Effect .

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Coriolis Effect

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Cyclotron Resonance

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Double Slit Experiment

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Elastic and Inelastic Collisions .

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Electric Fields

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Gauss's Law of Universal Gravity .

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Gravity - Force and Acceleration

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Ideal and Non-Ideal Gas Laws (van der Waal)

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Kinetic Theory of Gases .

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Kirchoff's Laws

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Maxwell's Equations .

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Moments and Torque

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One Dimensional Wave Equation .

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Pascal's Principle

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Phase and Group Velocity

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Poiseuille's Law

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Refractive Index

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Rotational Dynamics

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Simple Harmonic Motion

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Specific Heat, Latent Heat and Calorimetry

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The Laws of Thermodynamics

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The Zeeman Effect .

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Young's Modulus

Climate Change

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Keeling Curve .

Cosmology

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Cosmic Background Radiation and Decoupling .

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Friedmann-Robertson-Walker Equations .

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Inflation Theory

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Introduction to Black Holes .

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Olbers' Paradox .

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Stephen Hawking's Last Paper .

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Stephen Hawking's PhD Thesis .

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The Big Bang Model

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Vacuum Energy .

Finance and Accounting

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Brownian Model of Financial Markets .

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Capital Structure

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Dividend Discount Formula

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Lecture Notes on International Financial Management

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Periodically and Continuously Compounded Interest

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Repurchase versus Dividend Analysis

Game Theory

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General Relativity

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Basis One-forms .

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Catalog of Spacetimes .

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Curvature and Parallel Transport

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Einstein's Field Equations

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Gravitational Waves

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Hyperbolic Motion and Rindler Coordinates .

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Quantum Gravity

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Ricci Decomposition .

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Stress-Energy-Momentum Tensor .

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The Area Metric

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The Dirac Equation in Curved Spacetime .

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The Equivalence Principal

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The Essential Mathematics of General Relativity

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The Induced Metric

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The Light Cone .

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The Metric Tensor .

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The Principle of Least Action in Relativity .

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Vierbein (Frame) Fields

Group Theory

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Basic Group Theory .

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Basic Representation Theory .

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Building Groups From Other Groups .

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Sets, Groups, Modules, Rings and Vector Spaces

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Symmetric Groups .

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The Integers Modulo n Under + and x .

Lagrangian and Hamiltonian Mechanics

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Classical Field Theory .

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Euler-Lagrange Equation .

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Ex: Newtonian, Lagrangian and Hamiltonian Mechanics .

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Hamiltonian Formulation .

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Liouville's Theorem

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Symmetry and Conservation Laws - Noether's Theorem .

Macroeconomics

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Lecture Notes on International Economics

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Lecture Notes on Macroeconomics

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Macroeconomic Policy

Mathematics

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Amplitude, Period and Phase

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Arithmetic and Geometric Sequences and Series .

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Augmented Matrices and Cramer's Rule

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Binomial Theorem (Pascal's Triangle)

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Completing the Square

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Complex Numbers

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Composite Functions

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Conformal Transformations .

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Conjugate Pair Theorem

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Contravariant and Covariant Components of a Vector

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Derivatives of Inverse Functions

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Double Angle Formulas

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Eigenvectors and Eigenvalues

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Euler Formula for Polyhedrons

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Factoring of a³ +/- b³

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Fourier Series and Transforms .

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Gauss's Divergence Theorem

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Grassmann and Clifford Algebras .

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Heron's Formula

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Index Notation (Tensors and Matrices) .

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Integration By Parts

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Introduction to Conformal Field Theory .

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Inverse of a Function

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Law of Sines and Cosines

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Line Integrals, ∮

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Logarithms and Logarithmic Equations

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Matrices and Determinants

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Matrix Exponential

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Mean Value and Rolle's Theorem

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Modulus Equations

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Orthogonal Curvilinear Coordinates .

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Parabolas, Ellipses and Hyperbolas

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Piecewise Functions

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Polar Coordinates

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Polynomial Division

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Quaternions 1 .

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Quaternions 2 .

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Regular Polygons

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Similar Matrices and Diagonalization .

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Spherical Trigonometry

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Stirling's Approximation

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Sum and Differences of Squares and Cubes

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Tangent and Normal Line

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Taylor and Maclaurin Series .

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The Essential Mathematics of Lie Groups

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The Limit Definition of the Exponential Function

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Tic-Tac-Toe Factoring

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Trapezoidal Rule

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Volume Integrals

Microeconomics

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Marginal Revenue and Cost

Nuclear Physics

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Radioactive Decay

Particle Physics

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Feynman Diagrams and Loops

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Field Dimensions

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Helicity, Chirality and Weyl Spinors .

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Klein-Gordon and Dirac Equations .

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Regularization and Renormalization

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Scattering - Mandelstam Variables

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Spin 1 Eigenvectors .

Probability and Statistics

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Box and Whisker Plots

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Buffon's Needle .

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Categorical Data - Crosstabs

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Chebyshev's Theorem

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Chi Squared Goodness of Fit

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Conditional Probability

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Confidence Intervals

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Factor Analysis

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Hypothesis Testing

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Linear Regression

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Monte Carlo Methods

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Non Parametric Tests

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Pearson Correlation

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Permutations and Combinations

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Pooled Variance and Standard Error

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Probability Distributions

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Probability Rules

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Sample Size Determination

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Sampling Distributions

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Set Theory - Venn Diagrams

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Stacked and Unstacked Data

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Stem Plots, Histograms and Ogives

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Survey Data - Likert Item and Scale

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Programming and Computer Science

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How this site works ...

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More Programming Topics

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MVC Architecture

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Open Systems Interconnection (OSI) Standard - TCP/IP Protocol

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Public Key Encryption

Quantum Computing

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Density Operators and Mixed States .

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Entangled States .

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Quantum Field Theory

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Creation and Annihilation Operators

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Field Operators for Bosons and Fermions

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Lagrangians in Quantum Field Theory

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Path Integral Formulation

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Relativistic Quantum Field Theory

Quantum Mechanics

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Clebsch-Gordan Coefficients .

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Electron Orbital Angular Momentum and Spin

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Heisenberg Uncertainty Principle

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Ladder Operators .

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Multi Electron Wavefunctions .

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Pauli Spin Matrices

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Photoelectric Effect .

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Position and Momentum States .

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Probability Current

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Schrodinger Equation for Hydrogen Atom .

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Schrodinger Wave Equation

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Spin 1/2 Eigenvectors

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The Differential Operator

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The Essential Mathematics of Quantum Mechanics

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The Quantum Harmonic Oscillator .

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The Schrodinger, Heisenberg and Dirac Pictures

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The WKB Approximation

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Time Dependent Perturbation Theory

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Time Evolution and Symmetry Operations

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Time Independent Perturbation Theory

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Semiconductor Reliability

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The Weibull Distribution

Solid State Electronics

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Band Theory of Solids .

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Fermi-Dirac Statistics .

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Intrinsic and Extrinsic Semiconductors .

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The P-N Junction

Special Relativity

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Electromagnetic (Faraday) Tensor .

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Energy and Momentum in Special Relativity, E = mc² .

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Invariance of the Velocity of Light .

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Lorentz Invariance .

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Lorentz Transform .

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Lorentz Transformation of the EM Field .

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Newton versus Einstein

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Spinors - Part 1 .

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Spinors - Part 2 .

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The Continuity Equation .

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The Lorentz Group .

Statistical Mechanics

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Entropy and the Partition Function

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The Harmonic Oscillator

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String Theory

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Bosonic Strings

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Extra Dimensions

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Introduction to String Theory

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Kaluza-Klein Compactification of Closed Strings

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Strings in Curved Spacetime

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Toroidal Compactification

Superconductivity

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Bardeen–Cooper–Schrieffer Theory

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Introduction to Superconductivity .

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Superconductivity (Lectures 1 - 10)

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Superconductivity (Lectures 11 - 20)

Supersymmetry (SUSY) and Grand Unified Theory (GUT)

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Chiral Superfields

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Generators of a Supergroup

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Grassmann Numbers

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Introduction to Supersymmetry

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The Gauge Hierarchy Problem

The Standard Model

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Electroweak Unification (Glashow-Weinberg-Salam)

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Gauge Theories (Yang-Mills)

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Gravitational Force and the Planck Scale

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Introduction to the Standard Model

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Isospin, Hypercharge, Weak Isospin and Weak Hypercharge

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Quantum Flavordynamics and Quantum Chromodynamics

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Special Unitary Groups and the Standard Model - Part 1 .

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Special Unitary Groups and the Standard Model - Part 2

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Special Unitary Groups and the Standard Model - Part 3 .

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Standard Model Lagrangian

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The Higgs Mechanism

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The Nature of the Weak Interaction

Topology

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Units, Constants and Useful Formulas

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Last modified: January 26, 2018

Dispersion
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Dispersion occurs when pure plane waves of different wavelengths have different
propagation velocities. In the presence of dispersion, the wave velocity is no longer
uniquely defined, giving rise to the distinction of phase velocity and group velocity.

In a non-dispersive medium such as a vacuum, all frequencies of radiation, including
light, travel at the same speed regardless of wavelength. As a result a wavepacket will
not change shape as it travels.

In a dispersive medium different frequency components travel at different speeds.
As a result, a wavepacket spreads out because the longer wavelengths move faster and
the shorter wavelengths lag behind. So even if we start with a fairly localized particle,
it will soon loose this localization.

In the study of solids, the study of the dispersion relation of electrons is of paramount
importance. The periodicity of crystals means that many levels of energy are possible for
a given momentum and that some energies might not be available at any momentum. The
collection of all possible energies and momenta is known as the band structure of a material.
Properties of the band structure define whether the material is an insulator, semiconductor
or conductor.

Phonons are to sound waves in a solid what photons are to light: They are the quanta that
carry it. The dispersion relation of phonons is also important and non-trivial. Most
systems will show two separate bands on which phonons live. Phonons on the band that
cross the origin are known as acoustic phonons, the others as optical phonons.

The speed of a plane wave, v, is a function of the wave's wavelength:

v = λf

ω = 2πf

k = 2π/λ

=> ω = vk

Monochromatic light in vacuum: ω = kc

Monochromatic light in medium: ω = kc/n where n = refractive index.

Free, non-relativistic quantum mechanical particle of mass m: E_k = hω_k = h²k²/2m

=> ω_k = hk²/2m